Such drip irrigation systems and, in particular, emitter units for use therewith, have been known for some time. They involve the provision in the emitter of an elongated, flow-restricting flowpath through which water passes from the conduit so as to emerge from the conduit outlet as a substantially pressureless drip.
The construction and provision of this flow-restricting flowpath has in general fallen into two main categories, namely:
a) where the flowpath is entirely defined within an emitter housing; and PA1 b) where the flowpath is defined between the emitter housing and the surface of the conduit to which the housing, is bonded. PA1 (i) the provision of a plurality of superimposed interconnecting flow restricting flowpaths respectively separated by the membrane or additional membranes; PA1 (ii) the incorporation in the emitter unit of an effective non-return valve structure; and PA1 (iii) the provision of extended filtering arrangements.
The present invention is specifically related to the first of these categories, i.e. where the flowpath is defined within the housing. Furthermore, the invention preferably relates to such an emitter unit which is provided with flow control means, e.g., differential pressure control means, designed to ensure that the output rate from the emitter is substantially independent of variations in the pressure of the irrigation supply flow to the emitter unit.
Such a drip irrigation system and, in particular, irrigation emitter units for use therewith, have been disclosed in our earlier U.S. Pat. No. 4,210,287 (hereinafter "the '287 patent"). The '287 patent discloses an emitter unit provided with a resiliently flexible membrane which is releasably retained within a body member so as to serve a double function, namely, on the one hand, whilst being exposed to the irrigation flow pressure in the conduit to serve in exercising differential pressure control, and, on the other hand, to define, with respect to a flow restricting groove formed in the body member, a flow-restricting flowpath.
There have also been previous proposals for enclosing the emitter unit in a housing. These proposals have not included adequate solutions, if at all, in connection with problems which arise regarding the possible assembly of the constituent elements of the housing.
Particular problems clearly arise where, as in the case of emitter units the subject of the present invention, relatively long, elongated emitter units are required and means have to be provided for the retention together of the constituent pieces of the container prior to its bonding to the conduit, especially when the container is formed of relatively pliable plastic material (e.g. polyethylene) so as to facilitate its ready bonding to the conduit.
It is therefore an object of the present invention to provide a new and improved irrigation emitter unit for use in drip irrigation systems, wherein the above-referred-to requirement is substantially achieved.